Shopify.onCartUpdate

[follano]

Does this function fire when a product is added to cart through ajax? 

Shopify.onCartUpdate = function(cart) {

  alert('There are now ' + cart.item_count + ' items in the cart.');

};

I tried using it multiple time when a user adds product to cart and nothing is happening?

[xinghul]

Same question here, seems like it's not fired when items are added to the cart.

What is the best way to listen to cart updates using ScriptTag?

[manuelmontoya]

Same here, it looks like everybody is hijacking the "fetch" function to intercept the calls, but Shopify should have an API to avoid that.    

[coalescecreate]

Seems to work for me.

Added this mainly for people who have searched for Shopify.onCartUpdate

Some debugging ideas:

If you're working with someone else's theme maybe insert your script before the theme's script but after the vendors file.

Maybe your theme isn't using the Shopify library to update the cart. Below is one way to check.